Surface lapping machine

ABSTRACT

1,163,719. Lapping. J. BARRAGAN. 1 Dec., 1966 [18 Aug., 1966], No. 53821/66. Heading B3D. A surface lapping machine in which workpieces to be lapped are confined in rings placed on a rotatable bed of the machine and retained by arms of a stepwise rotatable device disposed in star formation, the angular extent of the steps of the motion of the rotatable device allowing the substitution of one ring by another at the periphery of the bed, and in which at least one plane, smooth table is disposed close to the periphery of the bed to permit the feeding of a ring to, and the withdrawal of a ring from, the bed by sliding, comprises (a) Means securing said rotatable device to a ratchet wheel; (b) A rotatable disc coaxial with the ratchet wheel; (c) Means limiting rotation of said disc to an angle equal to the angular extent of said steps; . (d) A pawl mounted on said disc and adapted to co-operate with the ratchet wheel; and (e) Means urging said disc to rotate in the direction opposite to the direction of rotation of the bed, said disc being more freely rotatable in the direction opposite to the direction of rotation of the bed than in the direction of rotation of the bed. A base (1) carries an annular table 2 surrounding a circular, flat, horizontally disposed bed 3 rotated by a motor housed in the base (1). Cylindrical rings 4 resting on the bed 3 contain the workpieces; these may be in contact with one another and the wall of the ring, may be arranged in cavities in a circular plate, or may be loaded by heavy covers 5 with handles 5a. Arms 8 each having two rollers 9 bearing against a ring 4 restrain the rings 4 from being carried round by the bed 3. Each arm 8 is secured to a jaw 12 of a three-jaw chuck 11 secured on a shaft 10; the jaws are displaceable radially by rotating the operating shaft 13 of the chuck by a square key. The flatness of the lopped workpieces is periodically checked optically, and the arms 8 radially adjusted accordingly to correct any curvature of the surface of the bed 3. At its upper end the shaft 10 is supported, through a height adjusting nut 15 and ball support 16, by a bracket 14. The shaft 10 has a bore 17 with a funnel 18 at the upper end to which abrasive in liquid suspension is supplied from the adjustable outlet 21 of a tube 20 carried in a support 22; the liquid suspension passes through a tube 19 to the bed 3. A ratchet wheel 24 is keyed to the shaft 10, and a disc 25 is rotatably mounted on the hub 24a of the ratchet wheel. A pawl 26 slidable in a radial groove in the disc 25 is engageable with the ratchet wheel 24 and has a tooth 26a engaging a notch 30a in a drum 30 rotatable by a handle 32 about a shaft 31 carried by the disc 25. The outer end of the pawl comprises a head 26b co-operating with an arcuate guide 34 to limit outward displacement of the pawl and a guide 35 tangential to the disc 25. A gap 36 in the periphery of the disc 25 receives a stop 37 fixed to the bracket 14, the angular extent of the gap less the angular width of the stop corresponding to the angular pitch of the teeth of the ratchet wheel, i.e. 60 degrees. The disc 25 is urged to rotate in the opposite direction to rotation of the bed 3 by a cable 38 carrying a weight 40. A portion 42 of the periphery of the disc 25 is toothed and meshes with a toothed sector 43 on a shaft 44. A pinion 45 on the shaft 44 meshes with a rack 47 on a piston 48 movable in a liquid filled cylinder 46. The ends of the cylinder are connected by a conduit 49 containing, in parallel, a non-return valve 50 and a constriction 51 adjustable by a knob 52. Operation.-With the bed 3 rotating in the direction of arrow F, the machine lapping workpieces in the three rings 4 and the pawl 26 in engagement with a radial flank of a tooth of the ratchet wheel 24, the thrust exerted by the rings 4 on the arms 8 tends to rotate the disc 25 in the direction of the arrow F so pressing the flank 36a of the gap 38 against the stop 37. When the handle 32 is actuated to withdraw the pawl 26 the weight 40 drives the disc 25 in the direction opposite to the arrow F; the piston 48 displaces liquid in the direction of opening of the valve 50, so that the disc 25 turns freely and the flank 36b of the gap 36 rapidly approaches the stop 37. The guide 35 drives the pawl 26 inwardly to engage the next notch of the ratchet wheel 24 whereupon the disc 25 may be driven by the ratchet wheel in the direction of the arrow F; the piston 48 displaces liquid through the constriction 51 to give hydraulic braking so that the advance through one step of the arms 8 is effected slowly, avoiding shocks and centrifugal force. Movement of the disc 25, upon liberation of the pawl 26, being rapid it is not necessary, in order to advance one step, to stop rotation of the bed 3 since the pawl 26 returns into engagement with the ratchet wheel before the assembly fixed to the shaft 10 has acquired acceleration. For safety reasons, the motor driving the bed 3 may be stopped as soon as withdrawal of pawl 26 commences, and the bed restarted only when the pawl has returned into engagement with the ratchet wheel and the flank 36b touches the stop 37; to this end, the pawl 26 is fixed to a curved bar 55 which acts on the push-button of a switch 56 in the supply to the bed driving motor, the length of the bar 55 being such that it frees the switch button only when the pawl has returned into engagement with the ratchet wheel. Two tables 57, 58 are mounted on the table 2 spaced 60 degrees apart around the bed 3. Each table comprises a sheet of hardened glass or of a smooth polished ceramic resting on four height-adjusting screws 60, the sheet being held down on the screws by spring-loaded draw members. The edges of the tables facing the bed are shaped to correspond to the curved edge of the bed; they may be lapped to the desired shape by contact with the edge of the bed 3 with abrasive interposed. The unloading table 57 is slightly below the bed 3. The loading table 58 may be above the bed and may be provided with a handle (65) so that after it has been used to feed a loaded ring on to the bed it may be spaced from the bed so as not to interfere with the edge of a ring which projects beyond the edge of the bed.

July 22, 1969 J. BAR'RAGAN 3,456,393

SURFACE LAPPING MACHINE v Filed Feb. 5, 1967 s Sheets-Sheet i July 22, 1969 J, R G 3,456,393

SURFACE LAPI ING MACHINE Filed Feb. 3, 1967 3 Sheets-Sheet S July 22, 1969 J. BARRAGAN SURFACE LAPPING MACHINE 3 Sheets-Sheet 3 Filed Feb. 5. 1967 N N N United States Patent 3,456,393 SURFACE LAPPING MACHINE Jacques Barragan, 144 bis Ave. General Leclerc, Sceaux, Hauts-de-Seine, France Filed Feb. 3, 1967, Ser. No. 613,940 Claims priority, application France, Aug. 18, 1966,

int. (31.13241; /00

U.S. Cl. 51-429 5 Claims ABSTRACT OF THE DISCLOSURE This invention relates to an improved surface lapping machine.

Surface lapping machines are already known which comprise a plane, horizontally disposed, circular lapping plate which is rotatably driven. On this lapping plate are distributed several cylindrical rings containing the workpieces to be lapped, which rings are prevented from being driven around with the lapping plate by arms provided with rollers, with the result that the rotation of the lapping plate causes the rings to rotate about their own axes. Thus the workpieces to be lapped are driven with a planetary movement with respect to the lapping plate on which they are lapped in a more or less short time by means of a fine abrasive.

Usually, at the end of each lapping cycle, the workpieces are unloaded from all the rings which are then loaded with new workpieces to be lapped. Owing to variations in shape of the workpieces and to the arrangement which it is suitable to impose on the workpieces in the rings, these unloading and loading operations are generally performed manually. Thus, during the stopping times necessary for loading and unloading the workpieces, the machine is unproductive. The present invention relates to a machine in which, by the provision of a loading and unloading device, the stopping times of the machine are extremely short.

According to the invention the arms intended to prevent the rotation of the rings are disposed in star formation and are carried by a stepwise rotatable device, the angular extent of the steps of the motion of the device allowing the substitution of one ring by another while at the periphery of the lapping plate, and at least one plane smooth table is disposed close to the periphery of the lapping plate to permit the feeding of a ring to, and the withdrawal of a ring from, the lapping plate by sliding. Preferably, two tables are used which are spaced apart around the lapping plate by said angular extent and the withdrawal or unloading table is situated a little below the lapping plate. If the rings do not project with respect to the lapping plate, the feeding or loading table may be situated a little above the bed.

Thus, without it being necessary to arrest the rotation of the lapping plate a ring may be caused to slide down from the lapping plate on to the unloading table and then, after rotation of the rotatable arm-carrying device through one step, a loaded ring may be caused to slide from the loading table on to the lapping plate into the location left empty by the preceding unloading. It therefore follows that, simply by providing a supplementary ring which is loaded in advance with workpieces, the withice drawal from the lapping plate of a ring with its lapped workpieces may be followed practically without interruption by the feeding on to the lapping plate of a ring loaded with workpieces requiring to be lapped.

Preferably, the angular extent of the steps of the motion of the rotatable arm-carrying device as well as the angular spacing apart of the two tables is equal to half the angular spacing apart of two rings on the lapping plate. In this way the handling distances are reduced and as will be described hereinafter the inertia forces due to the movement of the rotatable device may easily be limited.

In fact no driving force is necessary for driving the rotatable arm-carrying device through one step since, owing to the reaction thrust of the rings which tend to be driven by the lapping plate, this device tends to rotate spontaneously. Thus it is only necessary to provide intermittent braking of the device in order to produce its stepwise rotation.

The duration of the working cycle of the machine may be divided into a number of parts equal to the number of rings and the time for the complete lapping of the workpieces contained in a ring corresponds to the rotation of the arm-carrying device through one turn.

Preferably, the loading and unloading tables are made of hardened glass or of a smooth and polished ceramic having a hardness such that the grains of abrasive cannot penetrate it. Thus at the time of unloading of the workpieces which have been lapped, the latter are not scratched by sliding on a surface in which the abrasive grains have become encrusted. Furthermore, the cleaning of the glass or ceramic surfaces is very easy.

The invention will now be described in greater detail, by way of example, with reference to the accompanying drawings, in which:

FIGURE 1 is a schematic side elevation of a lapping machine according to the invention,

FIGURE 2 is a sectional plan taken on the line II-II of FIGURE 1,

FIGURE 3 is a vertical section, on an enlarged scale, of the central part of the machine,

FIGURE 4 is a section taken on the line IV1V of FIGURE 3, and

FIGURES 5 and 6 are sections taken on the lines VV and VIVI, respectively, of FIGURE 2.

The lapping machine shown in FIGURES 1 and 2 comprises an annular table 2 carried by a base 1, which table surrounds a circular, flat and horizontally disposed lapping plate 3. This lapping plate is rotatably driven in known manner at a speed of about one turn per second by means of a motor (not shown) housed in the base 1.

On the lapping plate 3 rest the cylindrical rings 4 in which are arranged the workpieces 6 requiring to be lapped. These workpieces, in known manner, may be in contact with one another and the wall of the ring, or else they may be arranged in cavities in a circular plate housed in the ring, or again, especially if they are light, they may be pressed by heavy covers 5 which are manipulated by handles 5a.

During rotation of the lapping plate 3 in the direction of the arrow F the carrying along of the rings and their contents with the lapping plate is prevented by ringretaining arms 8 each of which comprises two support rollers 9 bearing against ring which it retains. Due to the friction between the lapping plate 3 and the workplaces in the rings, the latter rotate around their axes in the direction of the arrows F Thus each workpiece confined in a ring performs, with respect to the lapping plate 3, a movement which displaces its surface of contact with the said lapping plate both radially and peripherally on the surface of the latter.

The arms 8 are supported by a shaft 10 coaxial with the lapping plate 3, which shaft is normally held stationary but may be displaced angularly in stepwise manner with respect to the lapping plate 3.

Preferably the arms 8 are mounted on the shaft 10 by means of a mechanism 11 which permits a certain controlled radial displacement of these arms. In the embodiment shown, in which only three rings are carried by the lapping plate 3, the mechanism 11 is in the form of a three-jaw chuck. Each of the arms 8 is fixedly secured to a jaw 12, which jaws are displaceable radially, in known manner (for example by means of a spirally threaded plate), by rotating the operating shaft 13 of the chuck using a square key (which shaft drives the threaded plate via a bevel pinion).

It is known that, in lapping machines of the kind to which this invention relates a critical adjustment of the positions of the rings is necessary if the lapping plate 3 is to remain flat, the lapping plate tending to assume a spherical shape, which may be either concave or convex. Periodic checking by optical methods of the flatness of the lapped workpieces obtained enables radial adjustment of the arms 8 to be made in the direction to correct the tendency of the bed to develop a curved surface.

At its upper end the shaft 10 is supported by a bracket 14 through the intermediary of a height-adjusting nut 15 and a ball support 16.

The shaft 10 comprises an axial channel terminating in a funnel 18 at the upper end of the shaft and extended at its lower end by a tube 19. Via this channel and the tube 19 an abrasive in liquid suspension can be fed to the lapping plate 3, the liquid being supplied to the funnel 18 from the adjustable outlet 21 of a supply tube which is carried in a support 22 which surmounts the shaft 10.

A ratchet wheel 24 (see FIGURE 4) is securely fixed to the shaft 10 by a key 23. On the tubular hub 24:: of the ratchet wheel a disc 25 is rotatably mounted. A pawl 26, slidable in a radial groove in the disc 25 in which it is maintained by a clamp 27 fixed to the disc by screws 28, is engageable with the ratchet wheel 24.

The pawl 26 carries a tooth 26a which meshes in a notch 30a in a drum 30 which is rotatable by a hand lever 32 around a shaft 31 carried by the disc 25.

At its radially outward end the pawl 26 comprises a head 26b intended to cooperate with an arcuate circular guide member 34 to limit the radially outward displace ment of the pawl and with the oblique portion 35 of said guide-member for urging home said pawl.

The periphery of the disc 25 has an indentation 36 formed therein which receives a stop 37 fixed to the bracket 14. The angular extent of the indentation 36 less the angular width of the stop 37 corresponds to the angular pitch of the teeth of the ratchet wheel 24, i.e. 60 in the present case where the ratchet wheel comprises six teeth (which is twice the number of the rings carried by the bed 3).

The disc 25 is urged to rotate in the direction opposite to the arrow F by a cable 38 tfixed to a point 39 on the periphery of the disc, which cable passes over a pulley 41 and has a weight attached to its end.

A peripheral portion 42 of the disc 25 is toothed and meshes with a toothed sector 43 secured to a shaft 44-. The latter also has a pinion 45 secured thereto which, in the interior of a cylinder 46, meshes with toothed rack 47 out longitudinally in the surface of a piston 48 movable in the cylinder 46. The latter is full of liquid and its two ends are connected in known manner, by a conduit 49, shown schematically, which includes two passageways in parallel, namely one containing a non-return valve 50 and one containing a constriction 51 the cross-section of which is adjustable by a knob 52. The hydraulic device comprising the items 44-52 is similar to that which is commonly employed to ensure the automatic and silent closure of doors.

The machine which has been described above functions in the following manner:

Let it be assumed that the lapping plate 3 is rotating in the direction of the arrow F, that the machine is performing a lapping operation on workpieces loaded in the three rings 4 and that the pawl 26 is in engagement with a radial flank of a tooth of the ratchet wheel 24. The thrust exerted by the rings 4 on the arms 8 is transmitted by the latter to the shaft 19 and exerts a torque on the latter in the direction of the arrow F; through the pawl 26 the thrust also tends to rotate the disc 25 in the direction of the arrow F, and consequently presses the flank 36a of the indentation 36 against the stop 37. The arms 8 are thus immobilised.

If the lever 32 is now actuated in the direction of the arrow E the notch 30a drives the pawl 26 radially outwards with respect to the disc 25.

As soon as the pawl 26 moves out of engagement with the tooth of the wheel 24 the weight 40 drives the disc 25 in the direction opposite to the arrow F. This causes rotation of the sector 43 in the anticlockwise direction, as viewed in FIGURE 4, and this results in the piston 48 moving in the cylinder 46 in the direction causing liquid to flow from the lower compartment of the cylinder 46 (as viewed in FIGURE 4) towards the upper compartment. Since this flow of liquid takes place in the direction of opening of the valve 50 and is not appreciably restricted, the disc 25 turns freely and the flank 36b of the indentation 36 rapidly approaches the stop 37. At the same time the guide member 35 drives the pawl 26 radially inwards into the following notch of the ratchet wheel 24.

With the pawl 26 once more in engagement with a radial flank of a tooth of the ratchet wheel 24 and the flank 36b of the indentation 36 touching the stop 37, the disc 25 may be driven by the ratchet wheel in the direction of the arrow F, This movement of the disc leads to rotation of the sector 43 in the clockwise direction, as viewed in FIGURE 4, resulting in a flow of liquid from the upper compartment to the lower compartment of the cylinder 46, which can only take place through the constriction 51. Thus the rotation of the assembly in the direction of the arrow F by the thrust of the rings 4 on the arms 8 is braked hydraulically (in addition to the effect of raising the weight 40) so that the advance through one step of the shaft 10 carrying the arms 8 is effected as slowly as desired, thus avoiding shocks and the effects of centrifugal force.

Since the movement of the disc 25, upon liberation of the pawl 26, may be very rapid, it is not necessary, in order to advance one step, to stop the rotation of the lapping plate 3 since the pawl 26 returns into engagement with the ratchet wheel before the assembly fixed to the shaft 10 has acquired a sufficient acceleration from the instant of liberation of the pawl.

Preferably the driving motor for the lapping plate 3 is stopped as soon as the withdrawal of the pawl 26 commences, and the restarting of the lapping plate only takes place when the pawl has returned into engagement with te ratchet wheel and the flank 36b touches the stop 37.

To this end the pawl 26 is fixed securely to a rigid bar 55 in the form of a sector of a circle of radius equal to that of the lapping plate 3, which acts on the push button of a switch 56 in the supply to the driving motor of the lapping plate 3. Two more switches (not shown) may be mounted one on each side of the stop 37, one cooperating with the flank 36a for a permanent feed and the other with the flank 36b ensuring a temporary feed for the return of the flank 36a into contact with the stop 37.

From the above description it will be appreciated that the rings 4 may be immobilised in the position shown in full lines in FIGURE 2 or in a position displaced 60 with respect to the latter.

Two tables 57 and 58 spaced apart by 60 around the lapping plate 3 are fixed to the annular table 2 so as to be opposite two of the rings 4 in their immobilised positions. Each of the tables 57, 58 comprises a sheet of hardened glass resisting on four height-adjusting screws 60. The glass sheets are held against the ends of the screws by draw members 61 influenced by springs 62; these draw members are housed in sockets 63 mounted in openings in the table 2 and secured by nuts 64.

The edges of the tables 57, 58 turned towards the lapping plate 3 are shaped to correspond with the curvature of the edge of the latter; they may be lapped to the desired shape by contact with the edge of the lapping plate 3 with the interposition of an appropriate abrasive.

By means of the screws 60 the table 57, which serves for unloading the rings 4, is adjusted for height so that its upper surface is a little below the level of the lapping plate 3, for example from two to three hundredths of a millimetre. This prevents any risk of a ring 4, and the workpieces which it contains, catching on the edge of the table 57 in its passage from the lapping plate to the table.

Conversely, the upper surface of the table 58, which serves to feed a loaded ring on the lapping plate 3, may be above the lapping plate if, in use, a part of the periphery of a ring projects from the table; the table 58 may be provided with a handle 65 so that after it has been used to feed a loaded ring on to the lapping plate 3 it may be spaced from the lapping plate so as not to interfere with the edge of a ring which projects beyond the edge of the lapping plate.

The employment for the loading and unloading tables of sheets of glass having a hardness comparable to that of the abrasive grains used for the lapping process prevents these grains from penetrating into the tables and from scratching the workpieces at the time of the unloading operation.

It will be appreciated that immediately a loaded ring is fed on to the table 57, this ring may be unloaded and placed on the table 58 with a view to receiving new workpieces requiring to be lapped. Thus a single supplementary ring ensures a quasi-continuous utilisation of the lapping machine irrespective of the number of rings in service.

What is claimed is:

1. A surface lapping machine in which workpieces to be lapped are confined in rings placed on a rotating lapping plate of the machine and retained thereon by radially extending arms provided with rollers which bear against the peripheral surface of said rings, wherein the improvement comprises a stepwise rotatable device coaxial with said rotating lapping plate and having said arms mounted radially extending therefrom, the angular extent of the steps of rotation of the device allowing the substitution of one ring by another at the periphery of said rotating lapping plate, and at least one plane, smooth table disposed close to the periphery of said rotating lapping plate to permit the feeding of a ring to, and the withdrawal of a ring from the rotating lapping plate by sliding, said stepwise rotatable device further comprising a ratchet wheel, a rotatable disk coaxial with the ratchet wheel, means limiting rotation of said disk to an angle equal to the angular extent of said steps, a pawl mounted on said disk to selectively engage with the ratchet wheel, means urging said disk to rotate in a direction opposite to the direction of rotation of the rotating lapping plate, and damping means operatively connected to said disk whereby said disk is freely rotatable in the direction opposite to the direction of rotation of the rotating lapping plate but controllably rotatable in the same direction as the direction of rotation of said rotating lapping plate.

2. A surface lapping machine according to claim 1, in which the means urging said disk to rotate comprises a weight attached to said disk by a cable and exerting a force tangentially to said disk.

3. A surface lapping machine according to claim 1, in which gear teeth are provided on said disk, a toothed sector mounted on a shaft with its teeth meshing with the gear teeth on said disk, a closed cylinder, a movable piston defining two compartments in said cylinder, said two compartments communicating with each other by two parallel fluid paths, one of which includes a non-retum valve and the other of which includes an adjustable constriction.

4. A surface lapping machine according to claim 1, comprising an electric switch mounted to cooperate with the pawl for interrupting the rotary motion of the lapping plate after each one step rotation by said stepwise rotatable device.

5. A surface lapping machine according to claim 1, in which the rotation of said disk is limited by a fixed stop engaging in a peripheral indentation in said disk.

References Cited UNITED STATES PATENTS 1,582,481 4/1926 Law 51131 X 1,723,961 8/ 1929 Wentz. 2,209,071 7/ 1940 Bullard 51-13 1 3,111,791 11/1963 Harris 51129 3,304,662 2/ 1967 Boettcher 51-13 1 FOREIGN PATENTS 985,552 3/1965 Great Britain.

HAROLD D. WHITEHEAD, Primary Examiner US. Cl. X.R. 51-131 

